The long-range objective of this project is to delineate the role and control of the vascular smooth muscle of the capacity vessels in the maintenance of cardiovascular homeostasis. The immediate objective is to measure changes in the capacitance vessel pressure-volume relationship resulting from sympathetic nerve stimulation and then to determine the magnitude of change following stimulation of the arterial pressoreceptors or the chemoreceptors. Test organs will include a loop of intestine, a garcilis muscle, spleen, liver or kidney. We will further evaluate and develop the the method of measuring vascular volume based on the product of mean-transit-time of an indicator and the rate of flow. Constant indicator infusion following a step input will be used rather than a slug injection. The time course of changes in volume resulting from changes in venous pressure, perfusion rate, sympathetic nerve stimulation and drug infusion will also be considered. Simulation techniques will be used to summarize the data.